Logo
FULL SITE MENU

Upper crankshaft bearing size?

F

flyingvranch

Member
I have a 1978 25hp block that I am rebuilding. The upper crankshaft bearing and seal machined openings appear to be a smaller size than normal. I have a bearing from another motor of the same type, but it is slightly larger than the opening on this block. The seal looks to be slightly too big also. They fit the crankshaft OK. On this block it has a part number 388709 but I cannot find this referenced anywhere. Any help would be appreciated!
 
388709 is not a part number... it is a casting number. Sorry, that doesn't tell us anything. You'll have to somehow pinpoint exactly what that block is for anyone to be of help.
 
Here are some photos of how the case opening is too small.

IMG_0991.jpg

Here is a comparison of the bearing openings to a normal 25 HP case on the right

IMG_0993.jpg
 
There were some changes in crankshaft bearings on early models.------35853R----Is the 35 HP model number.-----Parts book shows same bearing on 25 and 35 HP model cranks.
 
You're rebuilding a 1978 25hp via using a different crankcase is how it comes across to me.

The model number of 35853R indicates the new crankcase is a 1978 35hp model.

If I read this right... and parts installed in this 35853R crankcase (if that's what you're doing) will need to come from a 1978 35hp parts book. They may be available on this site via a parts lookup, but if not, let me know what you need.

I just looked... Yeah, it's all available on this site, a diagrams, C/shaft, bearings, whatever. Look into it.
 
Last edited:
Thank You everyone for the help so far. Here is a bit of background if this info will help someone identify my bearing. I bought a pristine vapor-cleaned 1978 35HP block from an Ebay seller. The parts are beautiful, the bores are perfect and I would very much like to use it in my rebuild if possible. Everything I have from the old 25hp motor fits perfectly so far except for this one top crankshaft bearing. I ordered a slew of various new parts already from this sight and I have started my rebuild. The pistons, new rings, and connecting rods all fit good on the new crankshaft and crankcase. Gaskets all seem to fit also. The one thing holding me up is the new bearing #386481 that I ordered does not fit this new crankcase hole. The hole diameter in this new case is 1.50".
I did look up the 1978 35HP motor parts on this site. It shows the crankcase, Top bearing, and seal to be the same part# as on the 1978 25hp also. So I am at a stopping point till I figure out this new bearing issue. I really would appreciate any insight or help if possible. The Ebay seller does not know either, so that is why I am looking for help here. One last thing, when this site sold me a gasket set that included the upper and lower seals they included an extra upper seal that is slightly small than the original 25hp seal. It does fit my new crankcase fortunately, so it look like I just need to locate this odd bearing size.
Sorry about the long winded post. Thanks again folks!
 
Last edited:
I just happened to have my books handy and the time to go thru them.

That top main bearing 386481 is the exact same for the 25 and 35hp from 1976 thru 1984... the change being made in 1975 & 1985... a starting search point of trial & error?
 
I think I have it figured out! The old block I have is a 1985 which has the larger bearing. The new block I have now that I want to use uses a 386481 thus the mismatch in sizes. Geeze it took me all day of head scratching to figure that out. Good thing I'm retired. LOL Thanks everyone for the help and thoughts!
 
If you had told us that the old block was a 1985 model previously instead of giving us the model number of 35853R (post #4) which indicated it was a 1978 35hp crankcase... the answer might have popped up sooner.

Red Foreman of the 70's show is looking for you!:rolleyes:
 
Last edited:
Point of clarity; The old donor block was an 85 model which I just discovered last night. It had no markings to identify it but I could tell by the connecting rods and wrist pin arrangement. I had previously thought it was a 1979 model before I figured that out finally. So it turned out that I had the larger bearing used in this model all along and I did not realize it.

The new block that I am assembling is a 1978 35HP crankcase. I am using some of the parts from the old 85 block to build this unit. The bearing I had was from the 85 model even though I thought it was the smaller. I ordered a new smaller bearing 386481 and it should fit just fine.
 
Back
Top